A like sealing device has been described in Dutch patent application 74,12131, which device is used for dispatching documents in transportation bags which mostly have the form of a flat envelope having along one of the edges a zip fastener which in closed position is sealed by means of the rupturable sealing member, on the one hand in order to render that the transportation bag can be opened less easily, but in particular in order to be able to establish afterwards that the transportation bag has been opened by a person unauthorized to do so.
With such a sealing device it should be possible to apply the sealing member quickly and without use of aids, and to clearly establish that the sealing member is broken.
In the sealing device known from this Dutch patent application the elastic means, which are deformed during insertion of the sealing member into the channel in the lock, are formed by resilient lips projecting from the shaft portion of the sealing member, and in the head of the sealing member there is formed a slit wherein a coin or special tool can engage for twisting said sealing member in order to break same.
It will be clear that this design leads to an increase of the cost price of sealing members.
The object of the invention is to provide a sealing device of the type as described above, in which no tool is required to break the sealing member thereof, while said sealing member is of simple construction and therefore can be produced cheaply.
According to the invention, for this purpose the resilient means are formed by a resilient portion of the channel wall, a boundary face of which serves as stop face for the enlarged free shaft end of unround configuration, which, when the sealing member is inserted, is received in a complementarily shaped channel portion, while the means for breaking said sealing member by twisting are connected with the pulling lip.
In a preferred embodiment of the invention for twisting the shaft of the sealing member there is rotatably connected with the pulling lip a disc which is provided with a recess for receiving secured against rotation the head end and/or the shaft portion connected to the head. The disc may be provided with a receiving cavity for the head of the sealing member and with an opening for passing an unround shaft portion thereof secured against rotation.
For breaking the seal one only need turn the disc, as a result of which the head end of the shaft of the sealing member is twisted relative to the free end extending in the channel secured against rotation until somewhere between head end and free shaft end the shaft is broken.
In order to avoid that upon breaking of the seal the broken-off end of the sealing member has to be removed from the lock before resealing can be effected, according to the invention the axial channel may extend throughout the lock. In that case the broken-off shaft portion falls from the bottom side of the lock. Nevertheless, in the sealing device according to the invention it is impossible to manipulate the sealing means or the resilient stop means from the bottom side in order to remove the sealing means without breaking same.
In order that the lock can be produced in a simple manner, and therefore cheaply, and be attached to a transportation bag, furthermore according to the invention it may consist of two essentially plate-shaped elements which, under inclusion of the material of the transportation bag at the end of the zip fastener, can be coupled together permanently be means of a snap-on connection in one or more places.